The invention relates to an inexpensive, simplified, mostly manual system for loading a plurality of boat loads of semiconductor wafers into a plurality of furnace tube is of a multi-level semiconductor processing furnace, and also to simultaneously protecting the wafer loading region from excessive heat emanating from open ends of the furnace tubes.
Commonly assigned U.S. Pat. No. 5,765,982 by Martin et al., issued Jun. 16, 1998 discloses an example of a fully automated prior art wafer boat loading/unloading system. FIG. 1A of U.S. Pat. No. 5,765,982 shows a complex loading station for a semiconductor processing furnace. A queue mechanism 30 having a stationary base is loaded with up to eight boatloads of semiconductor wafers. The queue mechanism shifts the right hand boatload of wafers to an index position at the right end of queue mechanism such that a pair of horizontal elevator tines of a vertical elevator mechanism can pick up one boatload of wafers at a time in the manner of a fork lift, and raise them upward and into alignment with one of a number of horizontal loading assemblies. Each loading assembly includes a carriage which moves horizontally on a track toward a semiconductor furnace tube located in a furnace cabinet on the right hand side of the furnace loading station so that up to eight boatloads of wafers supported on a horizontal cantilever paddle can be inserted into the hot zone of a corresponding furnace tube. A horizontal robotic mechanism is supported by vertical elevator. The horizontal robotic mechanism supports the tines which pick up one boatload of wafers and moves them horizontally to position each boatload of wafers, one at a time, over the paddle and lower it onto the paddle. After up to eight boatloads of wafers have been loaded onto cantilever paddle, the carriage supporting the paddle moves into the hot zone of the corresponding furnace tube. The entire operation is controlled by a controller 25 and an associated control console 15 which is mounted as shown. The foregoing system of U.S. Pat. No. 5,765,982 is very expensive.
The known fully automated wafer boat loading systems constitute one extreme of the prior art, and have been widely adopted by the larger semiconductor wafer fabrication concerns. The other extreme of the prior art constitutes manually loading/unloading all of the wafer boats, one at a time, wherein a worker, referred to as an operator, carries each wafer boat up or down a stepladder, supporting the loaded wafer boat by means of a conventional hand-held, fork-shaped xe2x80x9cpickup toolxe2x80x9d. This process is relatively inexpensive in that it requires very little capital investment, and is still widely used by smaller semiconductor wafer processing concerns. However, the fully manual loading/unloading technique has the shortcomings of being very stressful and dangerous for the operators, because each loaded standard wafer boat is very heavy.
The manual wafer boat loading/unloading technique also has the shortcoming that it puts the very valuable work product, i.e., the partially processed semiconductor wafers, at risk. One reason for this shortcoming is that if the operator becomes unsteady on the stepladder and drops a wafer boat, the economic loss is likely to be very high, perhaps many thousands of dollars. Another reason for the shortcoming is that during a completely manual wafer boat loading process, there is a substantial risk that the operator may mistakenly place one or more loaded wafer boats on the wrong cantilever paddle, which usually means that wafer boat gets loaded in the wrong processing furnace. Since different furnaces in the same multi-level rack of furnace tubes may be performing different processes, this mistake can destroy or result in a great loss of value of the in-process wafers.
It has long been known that most common injuries to operators performing fully manual wafer boat loading/unloading operations involve stumbling on the ladder steps or falling off of the ladder. The risk of this kind injury is greatly exacerbated by the substantial weight and precariousness of a boatload of wafers being held by means of a pickup tool and by the large amount of attention required to be focused by the operator on the task of maintaining stability of the boatload of wafers while climbing up or down the stepladder. The balancing act which the operator has to perform detracts substantially from the attention that needs to be given to safely climbing up and down the stepladder while supporting the wafer boat completely level.
Although the completely manual wafer boat loading technique and the automated wafer boat loading techniques have been known to those skilled in the art for many years, no one has ever provided a practical solution to the above described shortcomings of completely manual wafer boat loading/unloading processes other than to provide the above described automated wafer boat loading/unloading systems, which are very expensive.
Thus, there has long been an unmet need for a wafer boat loading system which is less costly than the highly automated systems of the prior art, and which is substantially safer than the known technique of manually carrying wafer boats up and down a stepladder to the higher cantilever paddles and placing the wafer boats thereon by means of a pickup tool.
Another problem associated with most, if not all, wafer boat loading/unloading techniques is that typically the temperatures within the furnace tubes often are from about 400 degrees to 1200 degrees Centigrade. Enough heat flows out of the mouths of the furnace tubes and through the adjacent openings of the scavenger device disposed between the furnace and the wafer boat loading station to cause the temperature in the vicinity of the wafer boat loading station to be too high for maintenance personnel, and also too high for operators who place wafer boats on the receiving queue or platform of the wafer boat loading station. When the temperature in the furnace tube reaches about 500 degrees Centigrade, then the region outside the furnace to mouth may become hot enough tube cause problems for control circuitry located in the region. One reason for this is that some transistors and sensing devices can not tolerate such high temperatures. For example, some integrated circuits that might be used in automatic wafer boat loading systems must be operated below 80 degrees Centigrade.
In the past, furnace tube caps have been used to seal the open mouths of semiconductor processing furnace tubes during processing of semiconductor wafers therein, but no practical technique has been provided for preventing heat from escaping through the open mouths of the furnace tubes and associated scavenger devices during wafer boat loading and unloading procedures.
Thus, there has been an unmet need for an apparatus and technique for preventing loss of heat through the mouth of a furnace tube and through an associated scavenger device into the working region of a multi-level wafer boat loading system, and for keeping the temperature in the working region low enough to be suitable for maintenance personnel and low enough to be suitable for operation of control circuitry associated with the wafer boat loading system.
Accordingly, it is an object of the invention to provide a simplified wafer boat loading device which reduces the amount of physical effort required for an operator to manually load/unload boatloads of semiconductor wafers into/from a multi-level semiconductor processing furnace.
It is another object of the invention to provide a wafer boat loading device which reduces the likelihood of physical injury to an operator who manually loads/unloads boatloads of semiconductor wafers into/from multi-level semiconductor processing furnaces.
It is another object of the invention to provide a simplified wafer boat loading system which requires a minimum amount of space in the vicinity of a multi-level wafer boat loading system.
It is another object of the invention to avoid the instability that results when an operator carries a boatload of semiconductor wafers up or down a ladder, using a conventional pickup tool.
It is another object of the invention to avoid operator fatigue resulting from carrying boatloads of semiconductor wafers up and down a stepladder to accomplish loading/unloading the boatloads of semiconductor wafers into/from a processing furnace.
It is another object of the invention to avoid the high cost of providing an automated semiconductor wafer boat loading system to solve the known problems associated with manual loading/unloading of semiconductor wafer boats to/from a cantilever paddle of a multi-level wafer boat loading station.
It is another object of the invention to avoid errors wherein an operator inadvertently loads a boatload of semiconductor wafers onto the wrong cantilever paddle of a multi-level wafer boat loading system.
It is another object of the invention to protect components of a wafer boat loading system from heat escaping through the mouth of a multi-level furnace and associated scavenger device during wafer boat loading/unloading operations.
It is another object of the invention to provide a wafer boat loading device which avoids injuries to operators due to repetitive motion, and meets OSHA standards for ergonomic devices.
Briefly described, and in accordance with one embodiment thereof, the invention provides an apparatus for assisting the loading of a plurality of wafer boats into a multi-level furnace (70) including a vertical arrangement of horizontal furnace tubes (71), by means of a multi-level wafer boat loading system (1) including a vertical arrangement of a plurality of horizontal cantilever paddles (5) supported by a plurality of the corresponding carriages (3) movable along corresponding horizontal tracks (4). A vertical elevator mechanism (10) is attached in fixed relationship to the wafer boat loading system (1). A vertically movable horizontal wafer boat platform (18B) is attached to a vertically movable carriage (31) which is included in the elevator mechanism and is vertically movable along a linear track (30) in the elevator mechanism in response to an electrical drive mechanism (22,27). A controller (25) for controlling the vertical elevator mechanism includes a memory storing a program and a processor coupled to the memory for executing the program to control the elevation of the platform (18B). The program is configured to store information representing a plurality of elevation levels of the wafer boat support platform (18B) adjacent to the plurality of cantilever paddles (5), respectively.
The program also is configured to receive a selection signal produced by manual selection of one of the elevator levels and to control the electrical drive mechanism (22,27) in response to the selection signal to move the wafer boat support platform (18B) from an initial position to the selected elevator level. The program is configured to receive manually entered information representing a plurality of elevation levels and to store the plurality of elevation levels in the memory. The controller (25) includes a touch pad display screen (16) adapted to display distinct touch pad areas corresponding to the elevation levels, respectively and produce the selection signal in response to pressing of one of the touch pad areas. The program also is configured to store information representing a home elevation of the wafer boat platform (18B) at a level which is safe and convenient for manual placing of the wafer boats, loaded with semiconductor wafers, on the wafer boat support platform (18B). The program also is configured to receive a home selection signal corresponding to manual selection of the home elevation. In one described embodiment, a scavenger device in communication with the multilevel furnace (70) includes a plurality of heat shield devices (50) each including a heat reflector plate (51) attached to a movable arm (52). The movable arm is attached to a carriage mechanism (56) and movable in response to a drive mechanism (54). A controller is operable in response to a first control signal to advance the heat reflector plate (51) in front of an opening (73) of the scavenger device adjacent to a mouth of a corresponding furnace tube (71) when the corresponding carriage supporting the cantilever paddle is in its xe2x80x9chomexe2x80x9d position. The control system also is operable in response to a second control signal to withdraw the heat reflector plate (51) from the opening (73) of the scavenger device to allow entry of the cantilever paddle into the interior of the furnace tube when the carriage supporting the cantilever paddle moves away from its home position toward the opening (73) of the scavenger device (72).